1. Field of the Invention
The present invention relates to ceramic material technology and more particularly, to a dielectric ceramic material, which uses binary oxides as initial powder materials and prepared in accordance with the corresponding proportion of the respective metal element.
2. Description of the Related Art
With the rapid development of technology, the direction of development of capacitor goes toward miniaturization, high capacity, high stability and high reliability. Nowadays, chip-based multilayer ceramic capacitor (MLCC) has been intensively used to substitute conventional capacitors, not only to reduce the size and increase the capacitor capacitance, but also reduce the production costs. So, multilayer ceramic capacitor is one of the currently mostly used electronic components in computers, mobile phones, automotive electronic devices.
According to different application ranges and electrical characteristics, US Electronic Industries Association (EIA) summarized capacitors as Class I temperature compensating type capacitors and Class II high dielectric constant capacitors whose capacitance is higher than that of Class I. The following Table I illustrates a capacitor specification constructed subject US Electronic Industries Association (EIA) Class II. For the advantage of high dielectric temperature stability, X8S (−55° C.˜150° C., ΔC/C≦22%) multilayer ceramic capacitor has been widely used in miniature electronic components and vehicles under a high temperature variation environment. Automobile electronic devices, such as engine control unit (ECU), anti-lock braking system ABS and proprietary digital electronic fuel injection system (PGMFI), need to operate in a fairly harsh environmental condition. Therefore, for safety reasons, when a multilayer ceramic capacitor to be applied to this fairly harsh environmental condition, it needs to have a more stable and higher temperature range (greater than 150° C.) of dielectric characteristic. Capacitor with ultra-high temperature stability will be essential elements for electronic systems for high temperature operation.
TABLE IUS EIA Class II Capacitor Specification TableLow Temp.SymbolHigh Temp.SymbolMax. %ΔC Symbol−55° C.X +45° C.3±1.0%A−30° C.Y +65° C.4±1.2%B−10° C.Z +85° C.5±2.2%C+105° C.6±3.3%D+125° C.7±4.7%E+150° C.8±7.5%F+200° C.9±10.0% P±15.0% R±22.0% S+22%/−33%T+22%/−56%U+22%/−82%VEx.: X7R −55~+125° C. ± 15% Y5V −30~+85° C. + 22%/−82%
Further, Barium Titanate (BaTiO3) has excellent dielectric characteristic, and is often used as a dielectric ceramic material for capacitor. However, in order to fit different application requirements, modifying agents may be selectively added to alter the electrical characteristics of barium titanate (BaTiO3). U.S. Pat. No. 7,751,178 discloses a ceramic dielectric of which the static capacitance-temperature characteristics can satisfy EIA-X8R specifications. This dielectric ceramic includes a perovskite type compound represented by the composition formula (Ba1−x−yCaxSny)m(Ti1−zZrz)O3 (where x, y, z, and m satisfy 0.9990≦m≦1.015, 0≦x≦0.20, 0.02≦y≦0.20, 0≦z≦0.05 respectively) as a primary component; and RE as an accessory component (where RE is at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), wherein 0.5 to 20 molar parts of RE is contained with respect to 100 molar parts of the primary component.
Taiwan Patent 1397090 discloses a dielectric ceramic composition of which the static capacitance-temperature characteristics can satisfy EIA-X8R specifications. This dielectric ceramic composition includes a BaTiO3 based primary component; and a glassy ingredient as an accessory component. The BaTiO3 based primary component includes the metal oxides of AO, MnO, B2O5 and Re2O3. Element A is selected from the group of Mg, Ca, Sr and Ba. Element B is selected from the group of V, Nb and Ta. Element Re is selected from the group of Y, Tb, Dy, Ho, Er, Tm and Yb. The glassy ingredient is composed of the oxide of SiO2—TiO2—XO wherein X is selected from the group of BaCa, SrMg, Z n and Mn.
Further, Taiwan Patent 201340146, issued to the present inventor, discloses a composite dielectric ceramic material that satisfies EIA-X8R and X9R specifications. This composite dielectric ceramic material includes (1−x)BaTiO3−xLiTaO3, (1−x)BaTiO3−xNaNbO3 and (1−x)BaTiO3−xBaCeO3 (in these three material groups, x: 0.01˜0.50). This invention also discloses a kind of high temperature stable dielectric ceramic material design principle that is based on the viewpoint of composite material to prepare a composite phase by mixing a dielectric material of high Curie temperature with a dielectric material of low Curie temperature. These two dielectric materials compensate for each other, wherein the dielectric material of low Curie temperature is based on the primary component of BaTiO3 of Curie temperature about 130° C.; the dielectric material of high Curie temperature is preferably over 200° C.
However, the aforesaid various dielectric ceramic materials commonly use BaTiO3 or Pervovskite compound as the primary component and at least one modifying agent, glassy ingredient or metal oxides (such as LiTaO3, Li2CO3 and Ta2O5) as an accessory component to alter the electric characteristics of BaTiO3, and to stabilize the rate of change of the temperature of the dielectric constant. However, these dielectric ceramic material systems need to use a ternary oxide (such as BaTiO3, LiTaO3 or Li2CO3) as the initial powder material and prepared in accordance with a predetermined ratio. The material is difficult to get and more expensive. Further, the manufacturing process of the dielectric ceramic material system is complicated or cumbersome, and other unnecessary compounds (such as Li3TaO4) can be produced during the manufacturing process, resulting in that the overall costs of the materials needed for the production cannot be effectively reduced. So, adding a predetermined ratio of compounds to barium titanate to prepare a dielectric ceramic material having ultra stable dielectric characteristics that comply with actual application is the major subject to be engaged in this industry.